The present invention relates to apparatus for monitoring the respiratory condition of a subject, and particularly for detecting the occurrence of apnea.
Reliable detection of apnea, namely a transient suspension of respiration, is a very serious problem which has not yet been successfully solved. Many techniques and devices have been developed for detecting apnea, but the known techniques are still not entirely satisfactory. Thus, some of the known systems monitor for apnea by detecting gross body movements, such as by the use of a mattress. However, in the event of an upper airway obstruction, such as by vomit or any other condition causing suffocation, the patient usually enters into twitching or other frantic movements during which no air passes through the lungs, but the physical activity prevents the actuation of the apnea alarm so that the apnea condition may go unnoticed until actual unconsciousness or death occurs. Other techniques for monitoring respiration in order to detect apnea include a thermistor or other transducer near the subject's nostrils to detect breathing, elastic tubes around the subject's chest to detect its expansion and contraction caused by breathing, or a microphone to detect the sounds produced by the subject when breathing. Such techniques, however, are not completely reliable particularly where the apnea is caused by an upper airway obstruction. About the only present technique for detecting apnea caused by an upper airway obstruction is by the use of a mask which monitors the CO.sub.2 exhaled by the patient, but this technique is very obstrusive; and moreover the mask tends to become clogged by mucous thereby losing its efficacy.